A computerized analysis of supersonic nonuniform flows over sharp and spherically blunted cones at angle of attack

A system of computer programs has been developed to predict supersonic inviscid and viscous nonuniform flow fields over sharp and spherically blunted cones at angle of attack. For blunt cones the flow fields considered were axisymmetric wake flows positioned such that the flow in the subsonic nose region remained axisymmetric. For sharp cones, both axisymmetric wake flows and two-dimensional shear flows were considered. The programs used in solving inviscid flow fields incorporate a modified inverse method for solving subsonic flow regions and modified axiymmetric and three-dimensional method of characteristics procedures for solving the supersonic flow regions. Body properties predicted by the inviscid solutions were used as edge data for solution of the corresponding laminar boundary-layers over the bodies. The viscous flow solutions were obtained using axisymmetric and full three-dimensional boundary-layer programs. Typical results from inviscid calculations have shown the development of strong adverse pressure gradients over both sharp and blunt cones in wake flows. In addition a thin entropy layer was found near the surface of both bodies; however, the normal pressure gradient was found to be negligible for the nonuniform flows considered. For the sharp cone in shear flow, property variation along the body was found to be almost linear. In all cases the aerodynamic coefficients were found to be significantly affected by the free-stream nonuniformity. Typical viscous flow field results have shown that relative to uniform flow values the skin friction and heat transfer increase along the windward streamline of both blunt and sharp cones in the nonuniform flows considered. Decreasing the width of the wake in wake flow increases the heat transfer and skin friction.     

Calculation of gas flow parameters around a reentry vehicle

An original numerical algorithm for calculating the gas parameters around a reentry vehicle was described and tested. It is based on a system of Quasi Gas Dynamics (QGD) equations and its approximations on hybrid meshes, which suppose adaptive, locally thickening meshes including both rectangular and triangular cells. The results of the calculations on a sequence of condensed meshes for Mach number values of 2, 5, and 12 are presented. These results correspond to well-known data and demonstrate the high efficiency of the algorithm.     

空间再入飞行体多传感观测融合仿真研究

空间飞行器再入飞行的可靠观测无疑是一个值得关注和探讨的问题。弹道导弹是一种典型的空间再入飞行器,其沿着预定弹道飞行,速度快,且可发生机动。对于弹道导弹的运动可以用较为简单和基本的运动模型的交互来近似,也可以用地面雷达和光学传感器来观测。将近似运动模型和观测值代入专门针对非线性估计问题的无味卡尔曼滤波(UKF)框架中,再利用数据融合算法,可以实现弹道导弹的航迹估计。文中首先描述了弹道导弹的运动模型,继而给出了不同传感器的量测方程和运动体的基本运动模型,然后阐述了交互多模型(IMM)、UKF及多传感数据融合算法,最后在仿真系统中实现航迹并得出结论。     

A comparison of several nonlinear filters for reentry vehicle tracking

This paper compares the performance of several non-linear filters for the real-time estimation of the trajectory of a reentry vehicle from its radar observations. In particular, it examines the effect of using two different coordinate systems on the relative accuracy of an extended Kalman filter. Other filters considered are iterative-sequential filters, single-stage iteration filters, and second-order filters. It is shown that a range-direction-cosine extended Kalman filter that uses the measurement coordinate system has less bias and less rms error than a Cartesian extended Kalman filter that uses the Cartesian coordinate system. This is due to the fact that the observations are linear in the range-direction-cosine coordinate system, but nonlinear in the Cartesian coordinate system. It is further shown that the performance of the Cartesian iterative-sequential filter that successively relinearizes the observations around their latest estimates and that of a range-direction-cosine extended Kalman filter are equivalent to first order. The use of a single-stage iteration to reduce the dynamic nonlinearity improves the accuracy of all the filters, but the improvement is very small, indicating that the dynamic nonlinearity is less significant than the measurement nonlinearity in reentry vehicle tracking under the assumed data rates and measurement accuracies. The comparison amongst the nonlinear filters is carried out using ten sets of observations on two typical trajectories. The performance of the filters is judged by their capability to eliminate the initial bias in the position and velocity estimates.     

Hybrid state estimation and model-set design of invariable-structure semi-ballistic reentry vehicle

Multiple-model approach is one of the main streams for hybrid estimation.The difficulty of this approach to estimate the hybrid state of the semi-ballistic reentry vehicle (SBRV) is model-set design.This paper proposes a quasi-Monte Carlo model set that can ensure the estimator near-optimal in the sense of minimum mean square error (MMSE).The SBRV has a high nonlinearity and its mode is spanned by multiple parameters with known bounds.The design methods and characteristics of the quasi-Monte Carlo model set...     

不变结构半弹道式再入飞行器的混合状态估计与模型集设计

多模型方法是混合估计的主流方法之一,以该方法估计不变结构半弹道式再入飞行器(SBRV)混合状态的难点在于设计有效的模型集.文中提出了一种伪Monte Carlo模型集可以使SBRV混合状态估计器在最小均方差(MMSE)意义下接近于最优.SBRV的再入估计具有高度的非线性,同时其模式由多个边界已知的参数张成.给出了这种伪Monte Carlo模型集的设计方法,并分析了其性能特征.该模型集相比于Monte Carlo方法生成的模型集有更高的精度,理论分析和仿真结果表明了新设计模型集的有效性与合理性.     

Control variable parameterisation with penalty approach for hypersonic vehicle reentry optimisation

An efficient trajectory optimisation approach combining the classical control variable parameterisation (CVP) with a novel smooth technology and two penalty strategies is developed to solve the trajectory optimal control problems. Since it is difficult to deal with path constraints in CVP method, the novel smooth technology is firstly employed to transform the complex constraints into one smooth constraint. Then, two penalty strategies are proposed to tackle the converted path and terminal constraints to decrease the computational complexity and improve the constraints satisfaction. Finally, a nonlinear programming problem, which approximates the original trajectory optimisation problem, is obtained. Error analysis shows that the proposed method has good convergence property. A general hypersonic cruise vehicle trajectory optimisation example is employed to test the performance of the proposed method. Numerical results show that the path and terminal conditions are well satisfied and better trajectory profiles are obtained, showing the effectiveness of the proposed method.     

Input-to-state-stability modular command filtered back-stepping attitude control of a generic reentry vehicle

A command filtered back-stepping attitude controller is exploited and analyzed to design a dynamic state-feedback controller for a generic Reentry Vehicle. A novel back-stepping control that obviates the need to compute analytic derivatives in the traditional back-stepping design is presented by combining command filtered back-stepping method, sliding-mode-based integral filters and inputto-state stability (ISS) analysis. The ISS-modular approach provides a simple and effective way for controlling non-linear Reentry Vehicle satisfying the strict-feedback form, simultaneously solving the problem of “explosion of complexity” in traditional back-stepping approach. The stability analysis of the closed-loop system and the convergence of the aerodynamic angles are verified based on the smallgain theorem. Numerical simulations are included to demonstrate the effectiveness of the proposed control scheme.     

Numerical solution of the three-dimensional boundary layer on a spinning sharp body at angle of attack

Numerical solutions for the laminar, compressible, three-dimensional boundary layer on general, sharp bodies of revolution at angle of attack with moderate axial spin are described. Unique solutions to the boundary layer equations are obtained by a finite-difference technique which properly treats the elliptic nature of the flow in a crossflow plane. Results are presented and compared with experiment for a tangent ogive-cylinder at four degrees angle of attack with and without spin. The results indicate that viscous flow solutions for spinning bodies at angle of attack can be obtained within the framework of conventional boundary layer theory. These solutions are free from the anomalies observed in a previous investigation.     

An implicit method for three dimensional viscous flow with application to cones at angle of attack

An iteration method for solving the implicit difference equations associated with three nonlinear parabolic differential equations is derived and analyzed. The method is applied to the high Reynolds number viscous flow around a cone at high angle of attack. The requirements which must be met to ensure convergence of the iterations are obtained. In addition, an analysis of the stability of the difference equations is presented and discussed. The numerical results are compared with experimental data for a 10° cone at 12° angle of attack, and a 5·6° cone at 8° angle of attack. The agreement is very good.     

飞机攻角侧滑角传感器检测系统

设计了一种新的飞机攻角侧滑角传感器检测系统。以MSP430F133单片机为基础,由伺服系统与反馈元件构造闭环的运动控制系统来精确定位,采用高精度A/D转换器(12位)提高测量精度,利用打印和显示模块输出数据,还可通过RS232接口与计算机通信,进行数据存档和综合分析。该系统具有操作简单、运行可靠、检测精度高等优点。     

Thermal stress analysis of laminated composite plates and shells

In this paper, Semiloof shell finite element formulation has been extended to thermal stress analysis of laminated plates and shells. The accuracy of the formulation has been verified using sample problems available in the literature. Thermal stresses in cross-ply and angle-ply laminated plates and shells subjected to thermal gradients across the thickness are presented for different boundary conditions, taking into account the temperature dependence of the material properties. The behaviour of laminates under thermal load is found to be different from that under mechanical loads in certain respects.     

Thermal stress analysis of skew plates by finite element method

Thermal stresses are induced in general due to nonuniform temperature distribution or due to the boundary restriction. Most of the work reported so far deals with either plates with edges clamped in plane of the plate or plates with stress free edges. While studying buckling or post-buckling problems, one should ideally analyse the plates with mixed in-plane boundary conditions. Hence, in the present analysis, thermal stress analysis of skew plates with mixed in-plane boundary conditions using finite element approach is attempted. In addition, the effect of in-plane boundary conditions on the thermal stresses is also discussed.     

汽车助力转向专用角度传感器设计

针对小型汽车电动助力转向（EPS）中的扭矩传感器进行研究设计,并制作了一种角度传感器,分辨率可达到0．08789°,具有低功耗、工作温度宽的特点。对设计制作出来的角度传感器进行了调试测量,由误差分析结果对角度传感器系统进行了改进,经改进后的角度传感器线性度良好,输出示值误差范围达到了所要求的精度。     

Neural network based adaptive fuzzy PID-type sliding mode attitude control for a reentry vehicle

This work investigates the attitude control of reentry vehicle under modeling inaccuracies and external disturbances. A robust adaptive fuzzy PID-type sliding mode control (AFPID-SMC) is designed with the utilization of radial basis function (RBF) neural network. In order to improve the transient performance and ensure small steady state tracking error, the gain parameters of PID-type sliding mode manifold are adjusted online by using adaptive fuzzy logic system (FLS). Additionally, the designed new adaptive law can ensure that the closed-loop system is asymptotically stable. Meanwhile, the problem of the actuator saturation, caused by integral term of sliding mode manifold, is avoided even under large initial tracking error. Furthermore, to eliminate the need of a priori knowledge of the disturbance upper bound, RBF neural network observer is used to estimate the disturbance information. The stability of the closed-loop system is proved via Lyapunov direct approach. Finally, the numerical simulations verify that the proposed controller is better than conventional PID-type SMC in terms of improving the transient performance and robustness.

     

Evaluation of a sliding mode observer for vehicle sideslip angle

This paper presents a sliding mode observer of vehicle sideslip angle, which is the principal variable relating to the transversal forces at the tire/road interface. The vehicle is first modelled, and the model is subsequently simplified. This study validates the observer using both a validated simulator and real experimental data acquired by the Heudiasyc laboratory car, and also shows the limitations of this method. The observer requires a yaw rate sensor and data about vehicle speed are required in order to estimate sideslip angle. Some properties of the nonlinear observability matrix condition number are discussed, and relations between this variable and observation error, vehicle speed and tire cornering stiffness are presented.     

车用氧传感器热应力场的数值分析

车用氧传感器是汽车电控系统的闭环控制（对空燃比）反馈信号发生器,它的作用是将汽车尾气中氧气的浓度信号发送到ECU（电子控制单元）,从而保持空燃比恒定为14．7左右。本文对一种典型的车用氧传感器在汽车启动时产生的热应力情况进行了数值分析,并采用大型通用有限元分析软件ANSYS得到了具体的分析过程和结果。     

基于压力传感器的迎角测量方法的研究

迎角是飞行器飞行的重要参数和弹箭飞行稳定性的主要技术指标。传统的迎角测量方法只适应于飞行器的迎角测量,而无法对高速旋转运动的弹箭进行测量。针对作高速旋转的飞行器,在以往迎角测量方法的基础上,提出了一种新的基于四象限压力传感器阵列的迎角测量方法。通过计算机仿真,验证了本方法的正确性,为旋转飞行器的迎角测量研究提供了一定的依据。     

DNS攻击分析和防范

DNS攻击事件层出不穷,DNS一直是网络安全中的一个薄弱环节,针对它攻击一直不断,本文对DNS协议的缺陷和攻击方式进行了分析,然后提出防范DNS攻击的方法和思路.